Pilot valve with unbalanced spool



United States Patent 3,542,075 [72] Inventor Neil W- Kroth 1,908,396 5/1933 Albright 137/625.69UX Joliet,|llinois 2,718,240 9/1955 Margrave l37/625.69 [2|] Appl. No. 731,114 3,081,060 3/1963 Thomas l37/625.69X [22] Filed May 22, 1968 3,203,246 8/1965 Horwitt etal. 137/556X [45] Patented Nov. 24,1970 3,229,851 1/1966 Horwitt et a1 137/556X [73] Asslgnee Caterpillar Tram Primary Examiner-Henry T. Klinksiek Pwflalmmis Auorney Fryer T'ensvold Feix Philli s& Lem io acorporatlon ofCalifornia J p p [54] PILOT VALVE WITH UNBALANCED SPOOL 5 Claims, 1 Drawing Fig. a [52] U.S.Cl. ..l37/625.69, ABSTRACT; A compact pilot valve having a ,ecipwcabk 251/320 spool Surfaces on the spool which interact with fluid in the Int Cl.

valve are unbalanced so flu d pressure ex snng [50] Field ofSearchW' l37/625.69, wlthm the plot valve tends to urge the Spool toward one end 12 0 of the valve A control element is preferably connected to the pilot valve spool so that the unbalanced spool 15 urged mm m- [56] Rem-Mes cited teractlon wlth the control to eliminate any free play or loose- UNITED STATES PATENTS ness developing in the coupling between the spool and its con- 743,985 11/1903 Koelkebeck l37/625.69

. 1 P Lo'rvALvEwrTn UNBAILANCED SPOOL The present invention relates to valves and particularly to I pilot valves .of the-type having a housing forming a bore in communication'with' fluid inlets and outlets. A spool is -reciprocably disposed in the bore and typically has a series of spacedapart lands in generally fluid sealing relation with the bow to regulate fluid flowacross the bore. l.arge numbers of these pilot valves are employed in various hydraulic circuits,

such'as thosefound onearthmoving machinery, with simplicity being desirable both fromthe standpoint of economy and compactness. Conventional "pilot valves'commonly employ spools having a balanced design which ismost readily characterized byf'land masses equally interacting withj fluid in the valve so that the spool tends to be repositioned only through an external control element.

, The present invention provides a more compact .valve having a reciprocable element arranged to regu'l ate'fluid flow through the va'lveand being o'f'unbalance'd design so'that fluid. within the valve tendsjto' continuously urge the reciprocable cleme'ntin'a selected direction, Preferably the reciprocable element, which may-be a spool, is of balanceddesign at least to the extent thatit interacts -with high pressure fluids while being unbalanced injithose portions susceptible to interaction with low pressure fluid. in addition to'pe rmitting substantial size reduction, the reciprocable element may beunbalanced so that fluid'within the valve tends to urge it into interaction with a control elementto eliminate free play or mechanical looseness in a coupling between the 'reciprbca ble element and the control element, Adjustment meansmay be employed in the coupling to regulate the relative within the valve housing. I

Other advantages and objects of the present invention are made apparent in the following description having reference to the drawing.

position of the spool The drawingis a partially sectioned view of a pilot valve I constructed according. to the'prefsentinvention-and having suitable control means coupled to its spool.

A pilot valve'is indicated atll in the drawing with its housing 12 defining acylindrical bore 13 for'recip'r'ocably receiving a spool l t Pilot fluid under relatively'high pressure from a 2 portion 29 of reduced diameter at the left end of the spool serves as a stop to limit leftward positioning of the spool within the bore 13.

' The unbalanced design of the'spool 14 is readily apparent from a consideration'of the arrangement of its lands 23, 24 and 26. The right end surface of the land 23 and the left end surface of the land 24 interact with and regulate the relatively high pressure fluid from the conduit 16 into one of the conduits 17 and 18, This portion of the spool is in balance since the reaction forces developed upon those two lands by the fluid are equal. Similarly, the right end surface of the land 24 and the left end surface of the land 26 interact with andregulate relatively low pressure fluid returning to drain from the conduit 18 and through the branch conduit 21. This portion of the spool is also balanced since the areas of theend surfaces of a the land interacting with the low pressure fluid are equal and reacts-with fluid passingto drain from the conduit 17 or existing in the leftjend of the valve bore 13 because of residual pressure in the sump 22 during-operation. Normal pressure in I the sump 22 maybe approximately 20 to pounds-per square inch, for example. I I II in addition to permitting size reduction of the-pilot valve,

the unbalanced arrangementbf the spool .1 4 serves an addi.

source (not shown is introduced into'the valve bore 13 by' means of an inlet conduit .16. A pair offluid outlet conduits l7 and 18 are in c omrnu'nication with the bore l3 'on each side of the inlet conduit 16. The r eciprocable spool l 4 permits selective regulation of fluid 'flow from the conduit 16 across the valve bore and into' 'oneof the conduits'l'7' and 18. Branch conduits l9 and 21 are in respective communication generally with the ends of the valve bore Both of the branch conduits l9 and-21 are in communication with a'fluid sump 22.

' The pilot valve ll is'of a typenormally employed for regu- I ing the other outletcondu'it l8 to drain across 'the valve-bore and through the=bratichconduit 21; Similarly for operation .of

the inotorin the'opp'ositedirection, the pilot-valve spool 14 is lating operation of: a double acting hydraulic motor (not shown) for'example -with which the conduits 1 7 and 18 are in t communication. With the pilot valvein the positionsho'wn in I P p Posmoned d to the outlet Passages 17 and As the groove 37 tends to.-move away from the valve housing lifted rightwardlyto communicateflth'e inlet conduit 16 with the outlet'conduit 18 and to permit free'communication from the conduit 17 to drain throughvthe v alve' bore 13 and'thebranch conduit 19.

Compactness of the pilotvalveis accomplishedthrough un-' balanced design'ofthe pilot valvespool 14 which permits'substantial reduction of theoverall length ofthepilot valve. To

regulate fluidiflow across the .valve bore l 3,"the spool 14 is" formed with three'landmasses 23:24 and 26. The land masses are formed and separated by'rnachining or otherwiseforming annular spaces 2? and 28 between each'pair of adjacent land masses respectivelyiln keepingwith the present invention, the

left end of thespool (as seenin the drawing) could readily be terminated at the left'side of the land mass' 23. Howeven 'the tional important function in view of the control element 31 connected to the right hand of the spool 'l4'by means of a coupling 32. The position of the-spool and operation of the pilot valve is regulated by the control element 31. Over extended periods of operation, the, connections 33 and;34 between the coupling and the spool 14 and control element 31, respectively, normally tend to develop free play or mechanical looseness so that the spool position is less accurately-responsive' tothe control element3l. With the spool 14 being unbalanced so-th at existing fluidpressure within the bore 13 continually urges thespool rightwardly, the connec-- tio n s 33 and 34 are maintained with a snug fit so that the spool position is very accurately-responsiveto the control element '31. The connecting niember 32'is providedwith adjusting means 36 forvarying-the length of the coupling 32. As free play develops in'the various connections; the coupling may be adjusted through the means 36 to maintain the relative position of the spool within the bore while the unbalanced design of the spool insures its accurate response to the control ele merit 31. To provide a visual indication of the amount of play developed in the coupling connections and 'the relative rightward shifting of the spool 14 to take up developed free play, a groove 37 is formed in the right end of the spool to be aligned with the right end .of the valve housing when the spool is in its neutral position as shown in the drawing and is over extended periods of operation, length of the coupling 32 is increased by adjustment of the means 36 to maintain the of the spool for regulating fluid flowproper relative position across the bore.-

Y Iclaim: I I

1. A reciprocable pilot valve, comprising:

a valve "housingd e'fining a cylindricalbore with fluid inlet and outlet means, said bo re being sealed atone end and having an opening at the other end;

a spool 'reciprocably arranged in the bore to regulate fluid flow across the bore said spoolincluding generally annular land masses which close with the bore for regulating.

fluid flow within thebore, the land masses defining annular land surfaces facing in opposite direction for interaction with fluid in the bore, said spool having one end surface adjacent the sealed end of the bore and exposed to fluid pressure within the bore for unbalanced reaction of the spool to the fluid pressure so that fluid pressure within the valve continuously urges the spool in one direction; and

control means operatively coupled with the spool, the unbalanced reaction of the spool to fluid pressure in the bore ore tending to maintain the spool in positive engagement with the control means.

2, The valve of claim 1 wherein an end of the spool opposite the one end surface of greater area extends from the valve housing and the control means are operatively coupled to the extended end of the spool, the coupling between the spool and the control means being susceptible to development of free play, fluid pressure tending to urge the spool toward the coupling to eliminate the free play developed in the coupling and further comprising means for indicating the amount of free play developed in the coupling and taken up by relative motion of the spool toward the coupling.

3. The valve of claim 2 further comprising means for adjusting the coupling between the control means and spool to maintain the relative position of the reciprocable spool within the bore.

4. The valve of claim I wherein the housing defines one inlet passage in communication with the bore for delivering relatively high pressure fluid, at least one outlet passage in communication with the bore for receiving the relatively high pressure fluid and at least one passage in communication with one end of the bore and with a normally low pressure region, the one end surface of the spool facing the one end of the bore adjacent the low pressure passage, the spool also including a pair of land end surfaces of effectively equal opposing area for receiving and regulating flow of relatively high pressure fluid from the inlet across the bore.

5. The valve of claim 4 wherein the valve housing defines two outlet passages on axially opposite sides of the inlet passage, another passage in communication with the normally low pressure region and generally with the opposite end of the bore, the low pressure region being a fluid sump, the one end surface of the spool regulating fluid flow across the bore and into the one sump passage from one of the outlet passages arranged generally adjacent thereto, the spool further defining another pair of land end surfaces of effectively equal opposing area for regulating fluid flow across the bore and into the other sump passage from the other outlet passage arranged generally adjacent thereto. 

